mid_13_ardu.ino

#include <SoftwareSerial.h>

SoftwareSerial BTSerial(2, 3);

const int ledPin = 9;
char indata;

void setup() {
  BTSerial.begin(9600);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  if(BTSerial.available()) {
    indata = BTSerial.read();

    if(indata == 'H')
      digitalWrite(ledPin, HIGH);
    if(indata == 'L')
      digitalWrite(ledPin, LOW);
  }
}